长江下游地区中更新世下蜀黄土沉积的古气候意义  

Xiashu Loess Deposits in the Lower Reaches of the Yangtze River and Their Paleoclimatic Significance

作　　者：程星宇 朱晓雨 蒲阳 何同 Cheng Xingyu;Zhu Xiaoyu;Pu Yang;He Tong(School of Geographic Sciences,Nanjing University of Information Science and Technology,Nanjing 210044,China;School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China)

机构地区：[1]南京信息工程大学地理科学学院,南京210044 [2]南京大学地球科学与工程学院,南京210023

出　　处：《热带地理》2023年第6期1049-1058,共10页Tropical Geography

基　　金：国家自然科学基金面上项目(41877284):东亚风尘钾长石矿物地球化学分布特征及其对早更新世东亚降雨演化过程的研究;国家自然科学基金面上项目(42171160):青海高寒牧区湖泊沉积物甾醇物源示踪及其对人类世GSSP确立的启示。

摘　　要：广布于长江中下游地区的下蜀黄土,是反映中国南方第四纪气候与环境变化的重要载体。下蜀黄土地层记录的多个古土壤条带与亚热带季风型湿润气候密切相关,然而古土壤形成的气候动力学机制尚不明确。文章对长江中下游位于老山山麓的2处下蜀土剖面的239个样品的磁化率进行分析,并充分结合已有的下蜀黄土年代地层学和磁性地层学研究,将2个新剖面与长江中下游广泛分布的下蜀黄土进行地层学比对,揭示了中更新世以来古土壤层的气候学意义。2个新剖面与已有研究的泰山新村剖面,在最近30万年发生的3个古土壤发生层(S1、S2和S3)上相对应,与镇江大港剖和江南老虎山剖面也十分相似,说明S1、S2和S3可作为下蜀土的标志层。基于地层磁化率与镇江大港剖面的比较,确立了地层年代控制点,进而分析古土壤层的厚度。结果显示,古土壤层厚接近甚至超过了下伏黄土。古土壤的沉积速率(6.2 cm/ka,n=19)大于黄土层(5.1 cm/ka,n=17)。这与中国北方黄土高原明显不同。结合已有对下蜀土的物源研究,古土壤的形成很可能与长江搬运作用以及河漫滩堆积过程有关。通过Sadler沉积动力模型检验,古土壤与黄土层在冰期和间冰期尺度上沉积连续,物源贡献并未间断。经过沉积速率校正,近50万年以来磁化率校正值曲线清晰显示了地球轨道偏心率10万年周期。全球冰量在轨道尺度上的变化很可能是古土壤形成的关键控制因素。Quaternary Xiashu loess deposits are widely distributed in the middle and lower reaches of the Yangtze River.The Xiashu loess deposits provide an important archive for studying the area's paleoclimate.We analyzed the magnetic susceptibility of 239 bulk samples from two newly excavated Xiashu loess profiles:the Puwulu and Pancheng.Based on a comparison with previously studied profiles in this region,our new record shows a good correlation in the stratigraphy,with three well-developed paleosols(layers S1,S2,and S3)as the marked layers.This correlation was observed in the Taishanxincun,Laohushan,and Dagang profiles.Despite the good spatial correlation in stratigraphy,the well-developed paleosol layers were thicker than the underlying loess layers.The average sediment accumulation rates in the paleosol layers(6.2 cm/ka,n=19)were higher than those in the loess layers(5.1 cm/ka,n=17).This stratigraphic feature of the Xiashu loess deposits differs from that of the Chinese loess plateau in North China.Combined with previous studies on the origin of the Xiashu loess deposits,the new records suggest a proximal origin;however,the dominant contribution of sediment materials from the floodplains at the foot of Laoshan Mountain.Increased material flux through the primary stream runoff on the floodplain resulted in higher sediment accumulation rates in the paleosols.Based on sedimentary model analysis,the paleosol and loess layers in the Xiashu deposits are continuous sedimentary records on glacial-interglacial scales.After adjusting for fluctuating sediment deposition rates,the revised magnetic susceptibility displayed a clear cyclic variation pattern,which was interpreted as the intensity of pedogenesis.Power spectral analysis suggests that the cyclic pattern of variations shows a strong frequency in the 100 kyr band for both the Pancheng and Puwulu profiles.This may explain the paleoclimatic dynamics of the paleosols that formed.The most developed paleosol layers(S1,S2,S3,S4,and S5)correlated well with the orbital parameter

关 键 词：下蜀黄土地层 磁化率 沉积速率 古土壤 全球冰量 长江下游地区 

分 类 号：P532[天文地球—古生物学与地层学]